The present invention relates generally to substrate processing chambers, and more specifically, to antenna coil assemblies for use with substrate processing chambers.
It has been found advantageous in the art of substrate processing used in making integrated circuits to utilize high density plasmas to enhance chemical deposition, etching, or cleaning reactions in a substrate or substrate processing chamber. It is known that inductively coupled plasma sources may provide high density plasma (e.g., 1.times.10.sup.11 to 2.times.10.sup.12 ions/cm.sup.3) and low energy bombardment of the processing surface (i.e., electron temperature T.sub.e of about a few electron volts or eV).
In some high density plasma substrate processing systems, a helical antenna coil is wound around the exterior surface of a dielectric (quartz) dome or cylinder forming a portion of the vacuum processing chamber. An RF current (i.e., from about 100 KHz to about 100 MHz) is passed through the antenna coil. When operated in a resonance mode with the applied RF power, an RF current (IRF) circulating in the antenna coil generates an axial RF magnetic field (B.sub.RF) within the processing chamber volume antenna coil. This magnetic field (B.sub.RF) induces a circulating RF electron current in the gas in the enclosed chamber to maintain a high energy plasma in the gas once the plasma is lit (i.e., once the gas becomes partially ionized by electron collisions). The configuration formed may be considered an RF transformer with the antenna coil acting as the primary winding and the plasma itself acting as the secondary winding.
In one commercially successful HDP chamber, the chamber utilizes a top coil and a side coil to enable tuning of the power delivered to the chamber and enhance uniformity of the plasma. The side coil is maintained within a sleeve to correctly position the coil relative to the processing chamber. The sleeve further includes a heating element to attempt to maintain constant heat throughout the sleeve.
Notwithstanding the success of the HDP system, improvements are desired. The thermal expansion and contraction of the sleeve caused by heat generated by the heating element and cooling performed by the antenna coil produce thermal stresses on the sleeve. Problems have arisen when the sleeve cracks under the stresses caused by this thermal cycling. Cracks in the sleeve can propagate to the coil, causing leakage of the cooling fluid and shutdown of the processing chamber.
It is desirable, therefore, to provide improved antenna coil assemblies, which alleviate at least some of the problems caused by thermal cycling stresses.